Вопрос Создаем модуль Joomla!

Джузеппе пишет: Как добавить еще одну вкладку в админке модуля?

<fieldset name="ADDITIONAL_FEATURES">

You can chain the attribute values of showon, using [AND], like so:

showon="field1:1[AND]field2:1"

Adding more fields to the chain is also allowed.
On a side note, you can use an [OR] clause in the chain too, adding more complexity, for example:

showon="field1:1[AND]field2:1[OR]fieldX:1"

Update for Joomla 3.7:
As of Joomla 3.7, you will be able to to use the ! operator (not equal to):

showon="field1!:1"

This means, if field1 does not equal 1.